Collect the first seven secret stars to unlock the last secret star in the final level. Some of the switches in that level can no longer be affected by time manipulation, allowing the last secret star to be collected and changing the ending.
Find all 60 puzzle pieces and complete the jigsaw puzzles on every World. The broken ladder that leads to the attic in the house where levels are selected will now be fixed. Climb up and enter the door to access World 1. Complete World 1 again to see the Epilogue. You can now revisit the Epilogue by walking into the hidden alcove on the left side of the title screen.
Every room in the Epilogue except for the last one has one or more objects that you can stand behind. Open the red journal on that screen and display its text. Stand behind one of the previously described objects. If done correctly, you will hear a sound and new text will appear. Note: If you open a green book, the red book will close and the text will disappear. Time manipulation must then be used to see all four new text.
Complete the following tasks to unlock the corresponding achievement. To view your achievements and stats in Steam, select "Community", then "My profile", then "View all my games", then the game and view stats.